Air to air heat pump apparatus



Aug. 21, 1956 R. H. BURGESS 2,75

AIR TO AIR HEAT PUMP APPARATUS File'd.Nov. 2, 1955 7 Sheets-Sheet 1 FIE.1

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AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2'. 1953 I 7 Sheets-Sheet 2 ZSV Z8-Z /00 7 Aug. 21, 1956 R. H. BURGESS 2,759,708

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AIR TO AIR HEAT PUMP APPARATUS Filed Nov. 2, 1955 'r Sheet s-Sheet ZFIE] 2/ z Aug. 21, 1956 R. H. BURGESS AIR TO AIR HEAT PUMP APPARATUS 7Sheeiis-Sheet 6 Filed NOV. 2, 1953 United States Patent AIR TO AIR HEATPUMP APPARATUS Russell H. Burgess, Chicago, Ill., assignor to Drying Systems, Inc, Chicago, 111., a corporation of Illinois Application November2, 1953, Serial No. 389,640

12 Claims. (Cl. 2573) This invention relates to air to air heat pumpapparatus and particularly to the control means for such apparatus.

In the use of air to air heat pump apparatus for conditioning air withina building, the wide range of heating and cooling requirements hasintroduced design and control problems which have in many instancesresulted in undue cost of manufacture or operation, or which haveresulted in unsatisfactory operation in other instances, and it is theprimary object of the present invention to improve the control means forsuch apparatus in such a way as to obviate the major diificu'lties andobjections heretofore encountered.

Thus in respect to the compressor capacity afforded in prior apparatus,it is well known that such capacity has been afforded by a singlecompressor of a size large enough to meet the maximum demands of thesystem. This of course puts a large star-ting load on the electric powerlines, and also results in short and frequent operating cycles of theapparatus with high starting loads imposed at frequent intervals on thepower lines. It is therefore a more specific object of the invention toenable smaller compressors to be used in multiple in such heat pumpapparatus, thereby to reduce the starting loads on the power lines andcause longer and less frequent operating cycles so as to correspondinglyreduce the number of starting loads placed on the power lines.

Another object of the present invention is to afford a normally inactivebooster heater in an air to air heat pump apparatus and to control thesame in such a way as to afford additional heating capacity when this isrequired and to supply heat in the inside air circuit during defrostingof the heat exchangers in the outside air circuit. An object related tothe foregoing is to provide for thermostatic control of such a boosterheater through the use of a subthermostat that senses the need for heatbeyond the capacity of the heat pump.

In an air to air heat pump apparatus one of the most troublesomeproblems has been the attainment of a satisfactory automatic defrostingcycle in respect to the outside heat exchangers, and in the past,various control expedients have been proposed and used. Thus suchdefrosting has been initiated by time controlled means which perform thedefrosting at predetermined intervals and in defrosting periods ofpredetermined length, re gardless of the need for such operations. Inother instances, air flow or air pressure in the outside air circuit hasbeen sensed to determine the need for defrosting, but such systems havealso been found to be unsatisfactory in many instances. It is thereforea further object of the present invention to improve the automaticdefrosting control in such heat pump apparatus, and related objects areto enable varying pressure conditions in the outside heat exchangers tocontrol the initiation and duration of the automatic defrostingoperations, to control the other elements of the heat pump apparatus tominimize the length of the defrosting periods, to control the boosterheater by the same means so as to prevent temperature drop in the insideair circuit, and to Patented Aug. 21, 1956 ice 2 enable such defrostingoperations to be accomplished at the minimum cost.

Other and further objects of the present invention will be apparent fromthe following description and claims and are illustrated in theaccompanying drawings which, by way of illustration, show a preferredembodiment of the present invention and the principles thereof and whatI now consider to be the best mode in which I have contemplated applyingthese principles. Other embodiments of the invention embodying the sameor equivalent principles may be used and structural changes may be madeas desired by those skilled in the art without departing from thepresent invention and the purview of the appended claims.

In the drawings:

Fig. 1 is a side elevational view taken partially in vertical sectionand illustrating a heat pump apparatus embodying the features of theinvention;

Fig. 2 is a view taken from the left in Fig. 1 and showing details ofinternal construction of the apparatus;

Fig. 3 is a view similar to Fig. 2 and showing additional details;

Fig. 4 is a fragmentary perspective view showing the sump and relatedparts of the base;

Fig. 5 is a sectional view taken substantially along the line 5- 5 ofFig. 4;

Fig. -6 is a sectional view taken substantially along the line 66 ofFig. 4;

Fig. 7 is a schematic view illustrating the refrigerant circuit;

Fig. 8 is a perspective View illustrating further details of therefrigerant circuit; and

Fig. 9 is a wiring diagram illustrating the electrical control circuitof the invention.

GENERAL ORGANIZATION For purposes of disclosure, the invention is hereinillustrated as embodied in an air-to-air heat pump apparatus 20 that issectionalized in its physical structure so as to facilitatetransportation and installation. Thus, the heat pump 20 comprises arelatively flat base unit 21, a blower unit 22 that rests on andcompletely covers the base unit 21, a compressor and heat exchange unit23 that rests on and completely covers the unit 22, and an upper ductunit 2 4 that rests upon the unit 23, and these sections or units may besecured in such relation by conventional fastening means such as screws,bolts or the like. The units 21, 22, 23 and 2-4 are so formed andrelated, as will be described in detail hereinafter, that a generally U-shaped inside air passage 25 is provided including heat exchangers 26and 27, and a generally U-shaped outside air passage 28 including heatexchangers 29 and 30 is provided. As will be hereinafter explained, thepresent apparatus may be set selectively for winter operation or summeroperation, and in the winter setting of the apparatus the heatexchangers 27 and 2'6 act as a common condenser in the refrigerantcircuit, while the heat exchangers 30 and 29 in the outside air circuitact .as a common evaporator. Conversely, in the summer setting of theapparatus, the heat exchangers 27 and 26 in the inside air circuit actas evaporators so as to cool the air in the inside air circuit, whilethe heat exchangers 30 and 29 in the outside air circuit serve as acommon condenser to dissipate heat to the air flowing in the outside aircircuit.

THE INDIVIDUAL SECTIONS OR UNITS The base 21 is formed primarily by twoend. channels 31 and two side channels 32 secured together so that theyrest on edge and define a rectangle. Midway between the side channels 32and parallel thereto, an elongated pan or sump 33 is mounted in fixedrelation to the end channels 31, and throughout a substantial portion ofits length the pan 33 is of the same depth as the base, as shown in Fig.1, while throughout the balance of its length the bottom of the panslopes upwardly so that it will drain toward the deep end. Within thesloping end portion of the pan 33 a central division wall is formed byan inverted U-shaped member 33F that has its lower edges fixed to thebottom wall of the pan and which has its closed upper end disposed inthe plane of the upper edges of the channels 31 and 32. At the left handend of the member 33F, Fig. 4, a cross plate 33E is extended across thepan 33 with its upper edge in the plane of the upper edges of thechannels 31 and 32, and its lower edge spaced from the bottom of the pan33 below the normal level of water that is maintained in the sump or pan33, as will be explained hereinafter.

The unit 22 is afforded by a plurality of square tubular frame members39 on which parallel end walls 41) and 41 and an intermediate wall 42are supported, the intermediate wall 42 being spaced from the end wall49 so that the intermediate wall 42 will be disposed directly over andwill engage the upper edge of the cross plate 33E, and on opposite sidesof the pan 33, this wall 42 rests on channels 44 which extend from theside channels 32 to the opposite sides of the pan. The unit 22 also hasside walls 45 and 46 and between the end wall 41 and the intermediatewall 42, a heavy insulated vertical wall 47 is provided which rests atits lower edge on the division wall 331 of the pan or sump 33. In thepresent instance the wall 40 is afforded by doors which extend the fullheight of the sections 22, 23 and 24 so that these doors or walls 40form the front or left-hand wall in Fig. 1, for all of the units. Theunit 22 is thus divided into a pump chamber 48 defined by the walls 40,42 and 46, an inside fan chamber 49 defined by the Walls 41, 42, 46 and47, and an outside fan chamber 50 defined by the walls 41, 42, 47 and45.

Within the pump chamber 48 a water pump 51 is supported with an intakepipe 51F projecting downwardly into the sump 33. This pump 31 is drivenby a motor 51M, and its discharge passes through a pipe 51D to its pointof use, as will be described hereinafter.

Within the inside fan chamber 49, an inside blower or fan 52 is mountedon support bars 52B, so that the discharge 52D of the fan opens upwardlyadjacent to the wall 47 Similarly, an outside blower or fan 53 ismounted on supports 53B in the chamber 50 so that the discharge 53D isdirected upwardly adjacent to the other side of the wall 47. The fans 52and 53 are driven by belt connections from drive motors 52M and 53 thatare supported from cross bars 52B and 53B in the chambers 49 and 50 ofthe unit 22. The chambers 49 and 50 constitute portions of therespective inside and outside air passages 25 and 28 and cooperatingportions of these passages are formed in part in the unit 23 and in partin the unit 24, as will now be described.

The unit 23 also has a framework formed from square tubular members 59closed at its forward end by the wall afforded by the doors 40 and onwhich an end wall 61 and an intermediate wall 62 are mounted in parallelrelation, so that the intermediate wall 62 is substantially above thewall 42. The unit 23 has side walls 65 and 66, and between the wall 62and the end wall 61, a thick insulating wall 67 is mounted so as to reston and form an upward continuation of the wall 47. Midway between thewalls 66 and 67 a vertical division wall 68 is extended parallel to thewalls 66 and 67 thus to afford a downward passage 25D between the walls66 and 68, and an upward passage 25U between the walls 68 and 67.Similarly, a wall 69 is mounted midway between and parallel to the walls65 and 67 to define a downward passage 28D between the walls 65 and 69and an upward passage 28U between the walls 67 and 69. In the lower endportion of the passage 28D, the heat exchanger 29 is mounted; in theupper end of the passage 28U the heat exchanger 30 is mounted; in thelower end of the passage 25D, the heat exchanger 26 is mounted; while inthe upper end portion of the passage 25D, the heat exchanger 27 ismounted; and these heat exchangers function in the operation of the heatpump system, as will be hereinafter described. Above the heat exchanger29 and in the passage 28D, a spray nozzle 75 is mounted and is connectedto the discharge 51B of the water pump 51 so that the heat exchanger 29may be caused to function as an evaporative condenser, as will bedescribed.

The passages 25U and 28H have their lower ends partially closed by crosswalls 63W and 69W, each of which has a relatively large opening therein,these openings being connected to the respective discharge ends of thefans 52 and 53 by flexible sleeves 52F and 53F.

The space defined by the walls 49, 62, 65 and 66 constitutes acompressor chamber and has bottom and top walls 81 and 82 so as toconstitute a closed chamber, and since the doors 40 may be opened atwill, an inside stationary wall 60 is provided just inside the doors 40.The wall 60, as well as all of the other walls defining the compressorchamber 80, are lined with sound absorbent material so as to eliminateobjectionable noise transmission. Within the compressor chamber 2'0,first and second motor driven compressors C1 and C2 are mounted, alongwith a considerable portion of the refrigerant piping and control meansincluding a four-way control valve 84 and a suction gas superheaterafforded by a heat exchanger 85 suspended above the coinpressors C-1 andC-2 and functioning as will be described hereinafter to dissipate andeffectually utilize the heat of the compressors.

The upper unit 24 of the structure is afforded by a framework made fromsquare tubular members 89 having its forward end closed by the walls ordoors 40 and having an end wall 91 and an intermediate wall 92 whichfalls substantially in the plane of the wall 62. Side walls 95 and 96are also provided and between these side walls a heavy insulateddivision wall 97 is provided which rests on and forms an upwardcontinuation of the wall 67. Between the Walls 96 and 97 a division wall98 is afforded which rests on the wall 68 and forms an upwardcontinuation thereof; and similarly, a wall 99 is afforded so as to reston and form an upward continuation thereof. The side wall 95 is arrangedin the present instance to afford an intake passage or opening 95Athrough which outside air may enter to pass downwardly through thepassage 28D, and the top of the unit 24- between the walls 95 and 96 isin this instance closed by a top wall 100. Between the walls 97 and 99the top wall 100 has a discharge opening 28-2 from which such outsideair may be discharged after use. Similarly, the top wall 169 closes theupper side of the unit 24 between the walls 96 and 98, while a dischargeopening 25-2 for the inside air circuit is afforded in the wall 100between the walls 97 and 98. The side wall 96, in the form shown, has anintake opening 96A formed herein to which the return pipe of theductwork may be connected. Within the passage 25D and in the spacebetween the walls 96 and 98, an air filter 101 is preferably positionedto filter the air passing through the inside air system. The inletopenings for the inside and outside air intake passages may, if desired,be provided in the top wall 100, as indicated in dotted outline at 295Aand 296A in Fig. 3, and in such an instance the corresponding intakeopening 95A or 96A,

or both, would be eliminated through the provision of imperforate sidewalls 95 and 96.

Within the inside air passage 25U and disposed above the heat exchanger27, an electric booster heater 105 is mounted so that this heater may berendered operative when additional heat beyond the normal capacity ofthe system is required, or during the defrosting cycle that will bedescribed hereinafter.

The water level in the sump 33 is maintained at a constant level throughthe provision of a water supply line 107 and a float control valve 108which, with its controlling float 108F, is mounted on the lower surfaceof the pump support platform. The sump 33 is also provided with anoverflow 169.

The sump 33 is arranged to receive and collect condensate that may beformed on any one of the heat exchangers 26 to 30, and for this reason adrip pan 110 is mounted in the outside fan chamber 49 beneath thesupport 53B, while a similar drip pan 111 is mounted in the inside fanchamber 50 beneath the supports 523. These drip pans slope toward thesump 33 and are arranged to discharge the collected water into the sump.

Within the inside air passage 25, and associated with the sump 33, is anupstanding humidifier plate 115 of an absorbent material, having awick-like action, and this plate is mounted so that its lower edge isdisposed in the sloping portion of the sump 33 below the normal waterline that is maintained therein. The humidifier plate 115 extendsupwardly for a substantial distance into the chamber 51 so as to besubjected to air flow, and is notched at 115N along its lower edge toafford clearance for the fan supporting bars 528. The humidifier plate115 attains its humidifying action in such a Way as to afford thedesired humidity in the inside air circuit within a range variation thatis satisfactory in many instances. Under other instances, however, itmay be desirable to attain a more accurate regulation of humidity, andin such an instance, the wall sections 68W in the inside air circuit areconstituted in the form of pans to which a constant but relatively smallsupply of water is supplied, and the control of humidity is attainedthrough the association of an intermittently operable electric heater1151-1 with each of the pans 68W. The manner of control of the heaters115H will be described in some detail hereinafter. It should be pointedout that any excess water that may be supplied to the pans 68W merelyoverflows onto the drain pan 111 so as to be discharged into the sump33.

THE ENCLOSED COMPRESSOR MEANS inside air system and, as will be furtherexplained, the

heat exchanger 85 in this arrangement serves as a super heater for thereturn refrigerant as it approaches the compressor.

THE REFRIGERANT CIRCUITS The 4-way valve 84 is of a well known type, andserves as the primary governing means for determining the flow path ofthe refrigerant in the present system. This 4-way valve is actuatedbetween its two positions by means of a pilot valve 841, which isshifted between its two effective positions by means of a solenoid 84S,and the way in which this solenoid is controlled will be describedhereinafter (see Fig. 7).

The refrigerant that is being returned to the compressors C-1 or (3-2flows from the 4-way valve 84 through a line 118 to one end of thesuper-heater 85, and any liquid components of the refrigerant that arethus fed to the super-heater 85 are evaporated within the superheaterand pass to a suction line 119 that has branches 119-1 and 1119-2, whichconvey the low pressure gaseous refrigerant to the respectivecompressors C-1 and C-2. The refrigerant gas is compressed within one orthe other, or both, of the compressors, the suction pressures of whichare equalized by an equalizing line 120. Compressor discharge is fedthrough high pressure lines 121-1 and 121-2 to a common hot gas line 121that extends to the 4-way control valve 84. In one setting of the 4-wayvalve 84, this hot gas is fed through a line 122 to the upper or intakeheader 30-1 of the heat exchanger 30 (see Fig. 8).

As it passes through the heat exchanger 30, the gas is subjected to acondensing action, and passes to a common header 29-30H whichconstitutes the lower header for the heat exchanger 30 and the upperheader for the heat exchanger 29. The gaseous and condensed portions ofthe refrigerant then flow to a lower header 29-2 of the heat exchangeunit 29, and pass through a pipe 124 to a 3-way hand valve 123 and to aline 125. This line includes a check valve 130, a filter-dryer unit 131and an expansion valve 132, from which the expanded gas flows to a 3-Wayhand valve 133 and through a pipe 134 to the lower header 26-2 of theheat exchange unit 26. The expansion valve 132 is controlled in aconventional manner by a control element 132C that is associated withthe return or suction line 118 (see Fig. 7). The refrigerant that isthus supplied to the heat exchanger 26 passes through this heatexchanger and a common header 26-2711 to the lower end of the heatexchange unit 27, and in passing through the unit 27, the evaporation issubstantially completed and the gaseous refrigerant and the remainingunevaporated portions thereof pass into an upper header 27-1 of the unit27 and through a return pipe 135 to the 4-way valve 84. The action ofthe system in the summer setting thereof is therefore to cool the airpassing through the inside air passage 25.

In the winter setting of the 4-way valve 84, the hot gases underpressure from the compressors pass through the line 135 and through theheat exchange units 27 and 26 in succession, so that the hot gas iscondensed, and since this condensing action is obtained by air flowthrough the inside air passage 25, this serves to heat the air in theinside air system. The condensed refrigerant then passes through theline 134 and the hand valve 133, but since it cannot flow through thecheck valve 130, this condensedor liquid refrigerant is transmittedthrough a line 136, a check valve 137, a filter-dryer unit 138, anexpansion valve 139 and a pipe 140 to the 3-way valve 123 from which itpasses through the line 124 to the lower header 29-2 of the heatexchange unit 29. This refrigerant then passes through the heat exchangeunits 29 and 30, and since for winter operation the system is set, aswill hereinafter be described, so as to supply such liquid refrigerantto the heat exchangers 29 and 3d at a temperature which is fifteen totwenty degrees below the minimum outside air temperature, therefrigerant will absorb heat from the air flowing through the outsideair system of the apparatus. This is effective to evaporate a largeproportion of the refrigerant, and this evaporated refrigerant, alongwith the entrained unevaporated portions thereof, will pass through theline 122 to the 4-way control valve 84 which in this winter settingtransmits the refrigerant to the suction line 118 and the superheater sothat after superheating, the gaseous refrigerant is returned to theintake of the compressor through the line 119. The expansion valve 139is governed in a conventional manner by a control unit 1390 that isassociated with the suction line 118 adjacent to the control unit 132C.

The pilot valve 84F has a control connection 84-1 to the main valve 84,and pressure connections for the pilot valve 84F are afforded by pipes84-2 and 84-3 extended respectively to the return line 118 and the highpressure line 121-1.

THE PRESSURE OPERATED CONTROLS For control purposes that will bedescribed in further detail hereinafter, a high pressure control line142 is extended from the high pressure line 121-1, and has a pressureoperated high limit switch 143 associated therewith. The line 142 alsohas a pressure operated switch 144 connected thereto for the purpose ofcontrolling the inside fan 52, as will be described. A pressure operatedswitch 145 is also associated with the high pressure line 142 for thepurpose of controlling the pump 51 that supplies water to theevaporative condenser, and this action will be described hereinafter.

A low pressure control line 146 is connected to the intake of thecompressor C-2 so as to be thereby associated with the suction line 119,and this low pressure line 146 has a pressure switch 147 associatedtherewith that is effective to control the operation of the secondarycompressor C-2 so as to start the compressor C-2 when the return linepressure is reduced to such a level as to indicate the need for addedcompressor capacity in the systerm.

A third control pressure line 148 is connected to the gas line 122 andthis line is utilized to govern the operation of a pressure switch 149which, in turn, serves as a primary control for governing the automaticdefrosting operation of the system. The pressure switch 149 is of thesnap acting type arranged at an adjustably set low pressure to snap toits low pressure position, and at an adjustably set high pressureposition to snap to its high pressure position. The pressure switch 149is connected to the line 148 through a check valve 150 and a springbiased relief valve 151 connected in parallel, the check valve 150 beingarranged to permit flow of gas from the pressure switch 149 to the line148, while the relief valve 151 is an adjustable spring-loaded valvearranged to prevent flow of gas from the pressure switch 149, and toallow flow of gas to the pressure switch 149 when the pressure of suchgas in line 148 reaches a predetermined value, and the relationship ofthe snap acting pressure switch 149, the check valve 150 and the reliefvalve 151 is utilized to govern the starting time and length of thedefrosting cycle and the pressure settings of the switch 149 and therelief valve 151 will be described hereinafter as they are related toeach other and to the refrigerant circuits attaining this result.

The pressure switches just described are included in the main electricalcontrol circuit of the system, as will now be described.

THE ELECTRICAL CONTROL CIRCUITS The electrical power for operating andcontrolling the present system is illustrated in Fig. 9 as beingafforded by a 220 volt cycle l-phase circuit having a common wire 160and two other wires 161 and 162. The compressor C1 is arranged to beenergized through a magnetic contactor C-1S, while the compressor C-2 isarranged to be controlled by a magnetic contactor G28, and these twocontactors are connected to the 220 volt l-phase circuit in aconventional manner, as illustrated in Fig. 9. Similarly,

the motor for the outside air fan 53 is controlled by a magneticcontactor 538, while the motor for the inside fan 52 is governed by amagnetic contactor 52S, and these contactors are connected to the 220volt l-phase circuit in the conventional manner. also afforded forcontrolling the inside air heater 105, and this contactor is alsoconnected in a conventional manner.

The magnetic contactors and the heater H constitute the primary elementsthat must be governed and controlled in the automatic operation of thepresent system, and such control is attained through a low voltagecontrol circuit that obtains its low voltage from a transformer 165, theprimary of which is connected between the wires and 161. The secondaryof the transformer is connected to leads 164 and 165 between which thevarious control circuits are disposed.

The primary setting control for the present system is afforded by a4-position rotary switch 166 that has its common contact connected tothe wire 164 by a wire 167. The settable contact for the switch 166 isafforded by a cross bar 166M that may be set in any one of fourpositions. In addition to the off position, the switch has an onposition, a winter position indicated by the letter W and a summerposition indicated by the letter S. In the winter position, the moveablecontact 166M Another contactor 1058 is extends circuit from the wire 167to two opposite W" contacts, and from the upper one of these W contactwires 168 and 169 extend in series to one end of a relay coil 170C, theother end of which is connected by a wire 171 to the wire 165. Wires 172and 173 extend from the wire 169 respectively to the on position and thesummer position so that when the cross bar 166M is in either the onposition, the winter position or the summer position, the coil 170C willbe energized. The other stationary W contact of the switch 166 isconnected by a wire 174 to a terminal 175, and between this terminal 175and the wire 165, a relay coil 176C is connected. Similarly, a relaycoil 177C and a relay coil 178C are connected in parallel between theterminal 175 and the wire 165. Thus, in the winter position of theswitch 166, the coils 176C, 177C and 178C will be energized, and this isin addition to the energization of the coil 170C.

Also connected in the low voltage circuit are the main sensing controlsthat sense conditions in the conditioned space for governing theoperation of the system. Thus, a main thermostat 180 is connectedbetween the wire 164 and a terminal 181, and relay coils 182C, 183C and134C are connected in parallel between the terminal 131 and the wire165. Thus, upon closure of the main thermostat 180, these three relaycoils will be energized. A humidistat 185 is also connected at one ofits terminals to the wire 164, and between the other terminal of thehumidistat the wire 165, a relay coil 136C is connected so that thiscoil will be energized when sensing of the need for humidificationcauses the humidistat 185 to close. A secondary or sub-thermostat 188 isconnected at one of its terminals to the wire 164 and from the otherterminal of the secondary thermostat 188, a relay coil 1870 is connectedto the wire 165. The thermostats 180 and 188 are of the type which closetheir contacts upon a drop in temperature to a predetermined level, andsuch thermostats may be of any conventional type arranged to afford aworking differential whereby the thermostat opens circuit at a slightlyhigher temperature level. The thermostat 180 is mounted in the usualposition on an inside wall of the building that is being conditioned,while the sub-thermostat 188 is mounted on the inside surface of anoutside wall and near the floor of a room. The location of thesub-thermostat 188 is preferably on the outside where the greatest heatloss may be expected, and the thermostat 188 is set about 5 degreesbelow the setting of the thermostat 180 so as to attain a highlyadvantageous heat control in winter, as will be explained.

The relay coils that have thus been described serve to controlcorrespondingly numbered relays shown in Fig. 9 which, in turn, governthe energizing coils of the different magnetic contactors.

Conditioning relays 170, 176, 177 and 178 are provided which are undercontrol respectively of the relay coils 170C, 176C, 177C and 178C, andall four of these relays are of the single pole double throw type, andare arranged so that the contact bars thereof are disposed normally inthe lower position shown in Fig. 9 and are actuated to their upperposition when their respective coils are energized. A wire 190 extendsfrom the wire 162 to one of the upper contacts of the relay 170, while awire 191 extends from the other upper contact of the relay 170, and hasbranch leads extended therefrom to one upper and one lower contact ofeach of the relays 176 and 177. The other lower contact of the relay 177is connected by a wire 193 to one end of the operating coil 52C of themagnetic contactor 528 of the inside fan 52. Thus, when the relay 170 isenergized and the relay 177 is de-energized, the inside fan 52 will beoperated, and this condition prevails when the main control switch 166is in its on position.

The other upper contact of the relay 177 is connected by a Wire 194 toone contact of the pressure operated switch 144, the other contact ofwhich is connected by a wire 194E to the wire 193. Thus, when the relay177 is in its upper or winter position, and the conditioning relay 170is in its upper or winter position, the inside fan is placed undercontrol of the pressure switch 144. With this arrangement, the insidefan remains inoperative until pressure in the compressor output line121-1 reaches a predetermined operative level so as to close thepressure switch 144.

The other conditioning relay 178 is connected by a wire 195 to the linewire 162, and this wire 195 has branches extending to one bottom contactof the relay 178. The other bottom contact of the relay 178 is connectedby a wire 196 to one contact of the pressure switch 145, and the wire197 extends from the other contact of the switch 145 to one terminal ofthe motor 51M, the other terminal of this motor being connected to thecommon line wire 160. The actuation of the relay 178 to its upper orwinter position renders the circuit to the motor 51M ineifeetive, butwhen the relay 178 is de-energized and its common contact is in itslower position, the pump circuit is conditioned for operation undercontrol of the pressure switch 145. This pressure switch is arranged toclose when pressure in the output line 121-1 of the refrigerant circuitbecomes too high, and this causes the pump 51M to pump water throughthespray, thus to cause the condenser 29 to operate as an evaporativecondenser.

Control relays 182 and 184 are also provided in the control circuit, andthese relays are of the single pole double throw type, and arecontrolled respectively by the relay coils 182C and 184C. One uppercontact of the relay 182 is connected by a wire 198 and a wire 199 tothe other upper contact of the conditioning relay 176, and the wire 199has an extension 199E that extends to the common contact of the pressureswitch 149. The other upper contact of the relay 182 and thecorresponding lower contact thereof are connected by Wires 200 and 201in series to one contact of the normally closed safety or overloadpressure switch 143, the other contact of which is connected by wire 202to a terminal 203. From this terminal, a Wire 204 extends to one contactof a normally closed thermostatic overload switch 205 that is located inthe compressor C1, and the other contact of this switch is connected bya contact 206 to one terminal of an operating coil C1SC that constitutesthe operating coil of the magnetic contactor C1S that governs thecompressor -1. The other terminal of this coil is connected to thecommon line wire 160.

From the terminal 203, a wire 207 is connected to corresponding upperand lower contacts of a conditioning relay 183 that is governed by therelay coil 103C. The other upper contact of the relay 183 is connectedby a wire 208 to the low pressure contact of the pressure switch 147,and a wire 209 extends from the common contact of the switch 147 to onestationary contact of a time delay relay 210. The other stationarycontact of this relay is connected by a wire 211 to a thermostaticallyoperated normally closed safety switch 212 that is included in thecompressor C2 and the wire 213 extends from the other contact of thissafety switch to an operating coil C2SC that serves as the operatingcoil for the magnetic contactor C2S. The other terminal of thisoperating coil is connected to the common line wire 160. The time delayrelay 210 has an operating coil 210C connected across the two stationarycontacts of this relay, and the operation is such that the relay 210 isclosed only after a predetermined period, thus to avoid concurrentstarting of the two compressors.

The other stationary contact of the pressure operated switch 147 isconnected by a wire 214 to the other lower contact of the relay 183, andthus the switch 147 causes operation of the second compressor inresponse to low pressure in the suction line 119 during the winteroperation of the system, and in response to high pressure in the line119 during summer operation of the system.

The other lower contact of the control relay 182 is connected by wires220 and 221 to the other lower contact of the conditioning relay 176,and a branch lead 222 extends from the wire 221 to one lower contact ofthe control relay 184. The other lower contact of the relay 184 and thecorresponding upper contact thereof are connected by a wire 223 to oneterminal of the operating coil 53SC, which serves to operate themagnetic contactor 538 that controls the outside fan 53. The otherterminal of the coil 538C is connected to the line wire 160. The otherupper contact of the relay 184 is connected by a wire 224 to the highpressure stationary contact of the pressure operated switch 149, and awire 225 connects this same contact to one terminal of the operatingcoil 848 of the magnetic pilot valve 84, the other terminal of thisoperating coil being connected to the wire 160. The other or lowpressure stationary contact of the switch 149 is connected by a wire 227to a terminal 228, and this terminal 228 is aiforded in the controlcircuit for the inside air heater 105. This inside air heater circuitmay be completed by movement of the pressure switch 149 to its lowpressure position, or through closure of the secondary of sub-thermostat188, and for obtaining control in response to the operation of suchthermostat, a relay 187 which is controlled by the coil 1870. Thus, awire 230 extends from the wire 199E to one stationary contact of therelay 187, and a wire 231 extends from the other contact of this relayto the terminal 228. From the terminal 228, a wire 232 extends to onestationary contact of a normally open holding switch 233 that isarranged to be moved to its closed position as an incident to theoperation of the magnetic contactor C-lS. A wire 234 extends from theother stationary contact of the switch 233 to one contact of a flowswitch 235 that is normally open and is arranged to be closed by airflow in the inside an passage 25. A wire 236 extends from the othercontact of the flow switch 235 to one terminal of an operating coil SCof the magnetic contactor 1058, the other terminal of this coil beingconnected to the wire 160. Thus, when the circuit is closed by theswitch 149 or by the relay 187, the inside air heater 105 will beeifective, it being understood, of course, that such operation can takeplace only when the conditioning relay 176 is in its upper or winterposition.

The heater H that is included in the humidifier has one terminalconnected by a wire 240 to the line wire and the other terminal of theheater is connected to one stationary contact of a normally open relay186 that is arranged to be closed by operation of the operating coil186C. The other stationary contact of the relay 186 is connected by awire 241 to one stationary contact of a holding switch 242 that isnormally open and which is arranged to he closed as an incident to theoperation of the magnetic contactor 528. A wire 243 extends from theother contact of the switch 242 to the line wire 162. Conventionalcircuit breakers, as shown, are used in the usual manner to protect allmotors and branch lines.

OPERATION Use and operation as air circulating and filtering meansDuring those periods when the heat pump apparatus is not required foreither heating or cooling purposes, it may nevertheless be used forcirculating and filtering the air in the building, and this isaccomplished by setting the main switch 166 to its on position. Thiscauses conditioning relay 170 to be operated so as to extend circuitthrough the wire 191, the lower contacts of the relay 177 and the wire193 through the coil 52C of the contactor 52S, and this closes thecontactor and causes operation of the inside air circulating fan 52.

Use and operation as a heating means in winter When the heat pump is tooperate as a heating and air conditioning means, the main control switch166 is set to its W or winter position. This causes simultaneousoperation of the conditioning relays 170, 176, 177 and 178 so as tolocate their contact bars in their upper positions of Fig. 9, andcircuit is extended from the upper contacts of the relay 176 through thewire 199 to one upper contact of the relay 182 so as to condition thisrelay 182 for thermostatically governed controlling action of thecompressor C1, and circuit is also extended through the switch 149,which is then in its left-hand or high-pressure position, and throughthe wire 225 to the control coil 848 of the 4-way valve 84, thus toactuate this valve to its normal winter setting in which the hotcompressed gaseous refrigerant from the compressors will be fed to theheat exchangers 26-27 in the inside air passage 25.

Operation of the conditioning relay 176 also extends circuit through thewire 224 to the upper contacts of the relay 184 so as to condition thisrelay for governing the outside fan 53. The relay 177, when thusoperated to its winter position, extends circuit to the pressure switch144, and this switch is arranged upon the operation of the compressormeans, to be closed by the resulting high pressure in the compressoroutput line 121-1, thus to energize the coil 52C and initiate operationof the inside air circulating fan 52.

Operation of the conditioning relay 178 merely serves to disable thepump 51 by breaking circuit to the pump motor 51M, and this insures thatthe pump 51 will not operate even though the pressure switch 145 mayclose.

Thus, the setting of the main switch 156 to its winter or 'v positioninitially results in setting of the 4-way valve 34 to its winterposition wherein the flow of hot gaseous refrigerant is normallydirected to the heat exchangers 2627 in the inside air circuit so thatthe heat exchangers 2627 act as condensers and serve to heat the air inthe inside circuit, and the condensed refrigerant is thereafter directedthrough the expansion valve 139 into the heat exchangers 2930 which actas evaporators so as to cause the refrigerant to absorb heat from theoutside air, and then through the 4-way valve 84- and the superheater 85where further heat is absorbed from the compressor compartment 80, afterwhich the hot gaseous refrigerant is returned to the compressor intakeor suction line 119.

The main thermostat 180 along with the humidistat 185 are mounted in theusual location on an inside wall of the space that is to be conditioned,and the secondary thermostat 138 is mounted on the inside face of anoutside wall of such space and near the floor level. The secondarythermostat 188 is thus in a position to sense those conditions whichresult in extremely rapid heat transfer through such outside wall. wouldbe brought about by a high wind, or an unusual drop in the outside airtemperature, and in the present system it has been found desirable toset the secondary thermostat 188 from three to five degrees below thesetting of the main thermostat 180.

When the system has thus been conditionsd for winter operation underautomatic control by the thermostats 130 and 133 and the humidistat 185,a drop in the temperature in the inside space below the desired levelwill cause closure of the main thermostat 189. This serves to operatethe rela s 182, 183 and 184. The operation of the relay 184 extendscircuit to the operating coil 538C thus to operate the magneticcontactor 53S and start the outside fan 53.

Operation of the relay 182 in response to the closure of the thermostat180 extends circuit to the coil CISC, thus to operate the magneticcontactor CIS so as to start the compressor Cl. Operation of thiscompressor builds up pressure in the output line 121 and serves to closethe pressure switch 144, and this energizes the coil 52C so as tooperate the contactor 52S and thus start the inside fan 52.

Operation of the relay 183 in response to closure of the main thermostat180 serves to condition the control circuit for the second compressorC2, but this second com- Such circumstances pressor remains inactivesince the pressure switch 147 is located in its high pressure orright-hand position as viewed in Fig. 9.

Such operation of the compressor C1 serves to initiate the heatingaction in the inside air circuit through the feeding of the hotcompressed gaseous refrigerant to the heat exchangers 26 and 27 in theinside air circuit, and in the event that the capacity of the compressor0-1 is insufiicient to accomplish the desired degree of heating, thisfact is reflected by a drop in the suction line pressure in the line119. This causes the pressure switch 147 to be shifted with a snapaction to its low pressure or lefthand position as viewed in Fig. 9, andthis completes circuit to the coil C2SC which serves to operate themagnetic contactor C2S. This results in starting of the compressor C-2,and hence the heating capacity of the system is increased. Thisincreased heating capacity is maintained until thermostat 130 issatisfied and breaks the circuit to relay holding coils 182C183C and184C. It will be recognized that the switch 147 may be of the adjustabletype so that the pressure differential required to cause a returnmovement of the switch 147 may be adjusted to meet conditions that maybe encountered in use.

If the heat losses from the space that is being conditioned areexceptionally high, due for example to high wind conditions or extremelylow outside temperatures, the secondary thermostat 138 will close, andthis causes operation of the relay 187. The relay 187, when thusactuated, extends circuit to the coil ZUSSC so as to operate themagnetic contactor 1058, and when this contactor is thus operated, thebooster heater is rendered operative so as to increase the overall heatoutput that is transmitted to the inside air circuit. When the need forsuch additional heat has been satisfied, the secondary thermostat 183will, of course, open and the booster heater will be tie-energized.

When outside air conditions are such that there is no appreciabletendency to form frost on the outside heat exchangers 29 and 30, thepressure in the return line 122 maintains a relatively constant value,as for example about 30 pounds per square inch, but when frost forms theheat exchangers 29 and 39, this pressure in the return line 122 mayreduce to a value of five pounds per square inch or even less, and sucha low pressure in the return line 12 2 clearly indicates that adefrosting operation is needed. The setting of the snap acting pressureswitch 149 is coordinated with the normal and abnormal pressure levelsthat are experienced in the suction line 122, such for example as thevalues hereinabove mentioned, and thus when the pressure in the line 122drops to a value of five pounds per square inch, the pressure switch 149will shift with a snap action from its normal high-pressure or left-handposition of Fig. 9 to its lowpressure or defrost position which is theright-hand position of Fig. 9. This shifting of the pressure switch 149initiates the defrosting action and the related functions in theapparatus. One of these related functions is the stopping of the outsidefan 53 so as to avoid dissipation of the defrosting heat that is to beapplied to the heat exchangers 29 and 30. This stopping of the outsidefan is caused by breaking of the circuit from the line 19913 to theupper contacts of the relay 184-. Another of the related functions isthe stopping of the second compressor C2 if this compressor happens tobe in operation at this time, and this is accomplished by the pressureswitch 147. In this respect, it should be pointed out that the reversalof the refrigerant flow, as will hereinafter be described, causes amarked increase in the pressure at the return line 119, and it is thisincrease in pressure that causes the switch 14-7 to shift from its lowpressure position to its high pressure position at this time.

When the switch 1 .9 shifts to its low pressure or right hand position,as viewed in Fig. 9, so as to institute the defrosting operation, itbreaks circuit to the wire 225 and the coil 848 of the 4-way valve 84,and this causes the valve 84 to return to its summer setting wherein thehot compressed gaseous refrigerant is fed through the line 122 anddirectly to the outside heat exchangers 29 and 30. This hot gas serves,of course, to accomplish the desired defrosting action, and the meltedfrost is drained downwardly onto the drip pan 110 so that it flows intothe sump 33, and any excess water collected in the sump will of coursebe discharged through the drain 1%.

It should be observed that when the hot gaseous refrigerant is fed intothe line 122, there is an immediate increase in pressure in this line,and this immediate increase in pressure may reach a level of 100 poundsper square inch, or even more. It will be realized, of course, that sucha pressure would be sufficient to return the pressure switch 14-9 to itshigh pres-sure or normal position since the switch 149 is set foroperation at about 30 pounds, and to prevent such immediate return ofthe switch 1&9 to its high pressure position, the relief valve 151 isset to a value substantially higher than the value of 100 pounds persquare inch that has been assumed hereinabove. The differential abovesuch a value is selected at a fairly high value that is somewhat belowthe value or pressure that will be reached in the line 122 when thedefrosting operation is completed. Thus, the pressure in the line 122will remain at about 100 pounds per square inch until such time as thefrost has been completely melted from the heat exchangers 29 and 30, andat this time the pressure in the line 122 will increase to about 200pounds per square inch, or even higher. Thus, the relief valve 151 maybe set so as to open at a pressure of about 175 pounds per square inch,and when defrosting has been completed, the resulting increase inpressure in the line 122 will open the relief valve 151 and cause thepressure switch 149 to be snapped back to its high pressure position.This will again set the 4-way valve 84 to its winter position, and whenthe pressure in the line 119 has been changed to its normal value, thepressure switch 147 will return to its low pressure position so as tocause the second compressor C2 to resume operation. Also, the outsidefan 53 will again be started.

In the course of a defrosting operation, the inside heat exchangers 26and 27 will no longer be supplied with hot gaseous refrigerant and, as amatter of fact, will be serving as evaporators. Hence at this time thereis a need for additional heat in the inside air circuit, and such heatis supplied by the booster heater 105, which is caused to operate solong as the switch 149 remains in its low pressure or right-handposition as viewed in Fig. 9. The circuit at this time is extendedthrough the wire 227 to the coil 1058C so that the magnetic contactor1058 is operated and the heater 105 is energized. Hence, when the switch149 returns to its high-pressure position to terminate the defrostingoperation, the circuit to the wire 227 is broken and the booster heater105 is deenergized and the system returns to its normal heatingoperation.

In winter use of the present apparatus, the humidistat 185 may, ofcourse, detect a need for humidification, and this closes circuit to thecoil 186C so as to cause operation of the relay 186. The relay 186 thuscompletes circuit to the heater 115E of the humidifier so as to raisethe temperature of the water in the humidifying pans and thus supply theneeded humidification to the air flowing in the inside air circuit.

Use and operation as a cooling means in summer When the heat pump is tooperate as a cooling and air conditioning means in the summer, the maincontrol switch 166 is set to its S or summer position. This causesoperation of the main conditioning relay 170, but it will be observedthat the relays 176, 177 and 178 remain in their lower or summerpositions. The 4-way valve 84 therefore remains in its normal or summerposition wherein the hot compressed refrigerant gases are 14 first fedto the outside heat exchangers 29 and 30 which act as condensers and aresubsequently fed through the expansion valve 32 and throu 1;h the insideheat exchangers 26 and 27, which act as evaporators so as to cool theair flowing in the inside air circuit.

When the circuit is extended through the relay to the relay 177, circuitis extended through the lower contacts of this relay to the coil 52C,which operates the magnetic contactor 528, thus to start the inside fan52. This inside fan runs constantly so long as the main switch 166 is inits summer setting.

The relay 176 extends circuit to the bottom contactors of the two relays182 and 184, and it will be observed that these two relays 182 and 184remain in their lower or unactuated positions, as shown in Fig. 9, solong as the temperature in the inside air space remains above the valuethat has been set on the main thermostat 180. Hence, under suchconditions, circuit is extended from the relay 182 to the coil C-TLSC sothat the magnetic contactor C18 is operated so as to cause operation ofthe compressor C-l. Circuit is extended from the lower contacts of therelay 184 to the coil 538C so that the contactor 538 is operated so asto cause operation of the outside fan 53. This will cause normaloperation of the system as a cooling means, and it might be pointed outthat if the cooling load on the system is excessive, the pressure switch147 may operate in the manner hereinabove described so as to bring aboutoperation of the second compressor C-2. Any condensate resulting fromsuch cooling is of course collected in the sump 33. In the event thatthe condensers action of the outside heat exchangers 29 and 30 isinsufficient, this may result in an excessively high pressure in theoutput or high pressure line 121, and in such an event, the pressureswitch 145 will be closed so as to energize the pump motor 51M, it beingnoted that this is possible during summer operation because of the factthat the relay 178 is in its lower or unactuated position. Operation ofthe pump 51 serves to pump water from the sump 33 and to spray thiswater over the heat exchanger 29, which thus serves as an evaporativecondenser and operates at increased efl'iciency.

When the inside air has been cooled to a sufficient extent, the insidethermostat 180 will close, and this serves to energize and operate therelays 182, 183 and 1845. The operation of the relay 182 stops thecompressor operation, while the operation of the relay 184 stops theoutside fan 53, and operation of the relay 183 stops operation of thesecond compressor C-Z in the event that this compressor has been inoperation.

CONCLUSION From the foregoing description, it will be apparent that thepresent invention affords improved control means for heat pumpapparatus, and that such improved control means eliminate the majordifficulties and objections heretofore encountered with apparatus ofthis character. It will also be evident that the present inventionenables a heat pump system to be operated with relatively smallcompressors utilized in multiple so that the power demands in startingof the compressors are relatively small, thereby to adapt the apparatusfor use in homes where high electrical starting loads are undesirable.It will also be evident that through the use of multiple compressors,the invention has enabled more eflicient operation of heat pump systemsto be obtained, and specifically it will be evident that through theattainment of longer and less frequent operating cycles, the maintenanceof the apparatus is materially reduced.

It will also be evident that the present invention attains a novel andeffective use of a booster heater in a heat pump system whereby thisheater acts to supplement the normal capacity of the system, and alsoserves to maintain the desired inside air temperature during defrostingoperations.

It will also be apparent from the foregoing description that the presentinvention enables an unusually efiective 15 and efficient defrostingaction which is automatic in character and which maintains thedefrosting time at the minimum, thus to nsure economy of operation ofthe system as well as satisfactory performance.

Thus, while I have illustrated and described the preferred embodiment ofmy invention, it is to be understood that this is capable of variationand modification, and I therefore do not wish to be limited to theprecise details set forth, but desire to avail myself of such changesand alterations as fall within the purview of the following claims.

I claim:

1. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main controlvalve in said refrigerating system having summer and winter settings forchanging said system from a cooling cycle to a heating cycle withrespect to said inside air passage, control means having a normalposition and a defrost position, means governed by said control meanswhen said control means is in its defrost position to shift said valvefrom its winter setting to its summer setting and to return said valveto its winter setting upon return of said control means to its normalposition, pressure operated means subjected to the pressure of thesuction gas outlet portion of said outside heat exchanger and operableupon said control means to shift the same to said defrost position whenthe pressure in said outlet portion falls to a predetermined minimumlevel indicative of a frosted condition, and to return said controlmeans to said normal position when the pressure in said portion rises toa predetermined high level indicative of completion of the defrostingaction, an air circulating fan in said outside air passage, andgoverning means for said fan including means operable to stop said fanwhen said control means are in said defrost position.

2. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, inside and outsideair circulating fans in said inside and outside air passages, fangoverning means normally effective to cause operation of said fansduring operation of said refrigerating system, a main control valve insaid refrigerating system having summer and winter settings for changingsaid system from a cooling cycle to a heating cycle with respect to saidinside air passage, control means having a normal position and a defrostposition, means governed by said control means when said control meansis in its defrost position to shift said valve from its winter settingto its summer setting and to return said valve to its winter settingupon return of said control means to its normal position, pressureoperated means subjected to the pressure of the suction gas outletportion of said outside heat exchanger and operable upon said controlmeans to shift the same to said defrost position when the pressure insaid portion falls to a predetermined minimum level indicative of afrosted condition, and to return said control means to said normalposition when the pressure in said portion rises to a predetermined highlevel indicative of completion of the defrosting action, said controlmeans being associated with said fan governing means and being effectiveto stop said outside fan when said control means are in said defrostposition, and a booster heater in said inside air passage renderedeffective by said control means when such control means are in saiddefrost position.

3. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main controlvalve in said refrigerating system having summer and winter settings forchanging said system from a cooling cycle to a heating cycle withrespect to said inside air passage, control means having a normalposition and a defrost position, means governed by said control meanswhen said control means is in its defrost position to shift said valvefrom its winter setting to its summer setting and to return said valveto its winter setting upon return of said control means to its normalposition, and pressure operated means subjected to the pressure of thesuction gas outlet portion of said outside heat exchanger including acheck valve through which gas may flow to said outlet portion andoperable upon said control means to shift the same to said defrostposition when the pressure in said portion falls to a predeterminedminimum level indicative of a frosted condition, and a pressurethreshold device comprising a relief valve through which gas may flowfrom said portion to said control means to return said control means tonormal position only when the pressure in said inlet portion rises to apredetermined high level indicative of completion of the defrostingaction.

4. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a magneticallycontrolled valve in said refrigerating system for changing said systemfrom a cooling cycle to a heating cycle with respect to said inside airpassage, a supplemental heater in said inside air passage, a mainsettable control switch governing said valve, a main thermostat and asupplemental thermostat, a pressure operated single-pole double-throwsnap switch subjected to the refrigerant pressure in the hot gas inletportion of said outside heat exchanger and having dominating control ofsaid valve to set said valve in its cooling position and to concurrentlyrender said auxiliary heater effective upon predetermined reduction ofthe pressure exerted on said switch, means controlled by said mainthermostat for rendering said system effective and ineffective, andmeans governed by said secondary thermostat for rendering said auxiliaryheater effective independently of said pressure switch.

5. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main valve insaid refrigerating system having a summer setting and a winter settingfor changing said system from a cooling cycle to a heating cycle withrespect to said inside air passage, a supplemental heater in said insideair passage, a main settable control for governing the setting of saidvalve, a main thermostat and a supplemental thermostat, a first pressureoperated means and operable thereby to a high pressure position or a lowpressure position, a pressure supply connection from the hot gas inletportion of said outside heat exchanger to said first pressure operatedmeans and including a pressure operated relief valve operable to preventtransmission of pressure to said first means until such pressure reachesa pressure several times the value of the high pressure value requiredto operate said first pressure operated means to its high pressureposition, a checked valved pressure return line connected in parallelaround said relief valve for allowing release of pressure from saidfirst means, means operated by said first pressure means to shift saidvalve to its summer setting when said pressure means is operated to itslow pressure position and to concurrently render said auxiliary heatereffective upon predetermined reduction of the normal pressure exertedthereon, means controlled by said main thermostat for rendering saidsystem effective and ineffective, and means governed by said secondarythermostat for rendering said auxiliary heater efiective independentlyof said first pressure operated means.

6. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main valve insaid refrigerating system having a summer setting and a winter settingfor changing said system from a cooling cycle to a heat 17 ing cyclewith respect to said inside air passage, a supplemental heater in saidinside air passage, a main settable control for governing the setting ofsaid valve, a main thermostat, a first pressure operated means andoperable thereby to a high pressure position or a low pressure position,a pressure supply connection from the 'hot gas inlet portion of saidoutside heat exchanger to said first pressure operated means andincluding a pressure operated relief valve operable to preventtransmission of pressure to said first means until such pressure reachesa pressure several times the value of the high pressure value requiredto operate said first pressure operated means to its high pressureposition, a checked valved pressure return line connected in parallelaround said relief valve for allowing release of pressure from saidfirst means, means operated by said first pressure means to shift saidvalve to its summer setting when said pressure means is operated to itslow pressure position and to concurrently render said auxiliary heatereffective upon predetermined reduction of the normal pressure exertedthereon, and means controlled by said main thermostat for rendering saidsystem effective and ineffective.

7. in an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main valve insaid refrigerating system having a summer setting and a Winter settingfor changing said system from a cooling cycle to a heating cycle withrespect to said inside air passage, a supplemental heater in said insideair passage, a main settable control for governing the setting of saidvalve, a main thermostat, a first pressure operated means and operablethereby to a high pressure position or a low pressure position, apressure supply connection from the hot gas inlet portion of saidoutside heat exchanger to said first pressure operated means andincluding a pressure operated relief valve operable to preventtransmission of pressure to said first means until such pressure reachesa pressure several times the value of the high pressure value requiredto operate said first pressure operated means to its high pressureposition, a checked valved pressure return line connected in parallelaround said relief valve for allowing release of pressure from saidfirst means, means operated by said first pressure means to shift saidvalve to its summer setting when said pressure means is operated to itslow pressure position and to concurrently render said auxiliary heatereffective upon predetermined reduction of the normal pressure exertedthereon, means controlled by said main thermostat for rendering saidsystem effective and ineffective, and means governed by said mainsettable control for reversing the controlling action of said thermostatconcurrently with the shifting of said main valve.

8. in an air to air heat pump apparatus having inside and outsideair-circulating passages and refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main controlvalve in said refrigerating system having summer and Winter settings forchanging said system from a cooling cycle to a heating cycle withrespect to said inside air passage, control means having a normalposition and a defrost position, means governed by said control meansWhen said control means is in its defrost position to shift said valvefrom its winter setting to its summer setting and to return said valveto its winter setting upon return of said control means to its normalposition, a first sensing means operaulc to sense the presence ofobjectionable frost on said outside heat exchanger and operable uponsaid control means to shift the same to said defrost position when suchobjectionable frost is sensed, a second sensing means responsive toreturn line pressure to sense completion of a defrosting operation andoperable to return said control means to said normal position whencompletion of the defrosting action is thus sensed, and

:18 a booster heater in said inside air passage controlled by saidcontrol means and rendered effective during each such defrostingoperation.

9. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, a main controlvalve in said refrigerating system having summer and winter settings forchanging said system from a cooling cycle to a heating cycle withrespect to said inside air passage, control means having a normalposition and a defrost position, means governed by said control meanswhen said control means is in its defrost position to shift said valvefrom its winter setting to its summer setting and to return said valveto 'its Winter setting upon return of said control means to its normalposition, a first sensing means operable to sense the presence ofobjectionable frost on said outside heat exchanger and operable uponsaid control means to shift the same to said defrost position when suchobjectionable frost is sensed, a second sensing means responsive toreturn line pressure to sense completion of a defrosting operation andoperable to return said control means to said normal position whencompletion of the defrosting action is thus sensed, a booster heater insaid inside air passage controlled by said control means and renderedeffective during each such defrosting operation, a main thermostaticmeans for controlling operation of said refrigerating system, and asecondary thermostat operable to control said booster heaterindependently of said control means.

l6. in an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, said systemincluding two compressors connected in parallel in the system, means forcontrolling said system including thermostatic means for starting andstopping a first one of said compressors, and means for starting andstopping the second one of said compressors including pressureresponsive means responsive to the suction pressure at the intake ofsaid first compressor, a main control valve in said refrigerating systemhaving summer and winter settings for changing said system from acooling cycle to a heating cycle with respect to said inside airpassage, control means having a normal position and a defrost position,means controlled by said control. means for de-energizing said secondcompressor whenever said control means is actuated to its defrostposition, means governed by said control means when said control meansis in its defrost position to shift said valve from its winter settingto its summer setting and to return said valve to its winter settingupon return of said control means to its normal position, a firstsensing means operable to sense the presence of objectionable frost onsaid outside heat exchanger and operable upon said control means toshift the same to said defrost position when such objectionable frost issensed, and a second sensing means responsive to return line pressure tosense completion of a defrosting operation and operable to return saidcontrol means to said normal position when completion of the defrostingaction is thus sensed.

ll. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system With heat exchangersin said outside and inside air-circulating passages, said systemincluding two compressors connected in parallel in the system, means forcontrolling said system including thermostatic means for starting andstopping a first one of said compressors, automatically operabledefrosting means for the outside heat exchangers, and means controlledby said defrosting means operable to stop said second compressor duringdefrosting operations.

12. In an air to air heat pump apparatus having inside and outsideair-circulating passages and a refrigerating system with heat exchangersin said outside and inside air-circulating passages, said systemincluding two compressors connected in parallel in the system, means forcontrolling said system including thermostatic means for starting andstopping a first one of said compressors, defrosting means for saidoutside heat exchangers, defrosting control means for initiating andterminating defrosting operations in respect to said outside heatexchanger, and means controlled by said defrosting control meansoperable to stop said second compressor during defrosting operations.

References Cited in the file of this patent UNITED STATES PATENTS2,049,625 Ruppn'cht Aug. 4, 1936 Crago Aug 1, Lodwig May 4, Graham June4, Lund Oct. 19, Cody Apr. 5, Backstrom Ian. 31, Clancy 90v. 21, VargoMay 12, Ditzler et al Mar. 23, Telkes May 4,

